The cardiovascular system consists of the heart and blood vessels as it primary organs, and functions to circulate blood throughout the body. The American Heart Association explains that the main cardiovascular organ, the heart, pumps blood through a tubular network of arteries that conduct oxygen, fluids, nutrients, immune cells and other important substances to every cell of the body including the heart itself. At the organs and tissues of the body the arteries divide into tiny thin-walled blood vessels called capillaries. The blood then travels back to the heart where it is pumped to the lungs to be oxygenated before being returned to the heart, ready for another cycle in the cardiovascular system.
The Heart
The heart is about the size of a clenched fist and beats approximately 75 times per minute. Each heartbeat pumps almost 80 ml of blood through the vascular system of the body. The right atrium of the heart receives oxygen-depleted blood from the body and passes it to the right ventricle chamber, which pumps it to the lungs through the pulmonary arteries, explains the Heart and Stroke Foundation. In the lungs, the blood is reoxygenated and returned to the left atrium of the heart where it is pumped to the left ventricle. The muscular walls of the left ventricle then pump oxygen-rich blood throughout the body to every cell. It takes a drop of blood only about one minute to travel through the body and back to the heart.
The Arteries
Arteries are large, thick-walled blood vessels that transport blood from the heart to the cells of the body. All the arteries carry oxygenated blood, except for the pulmonary artery, which carries deoxygenated blood from the right ventricle to the lungs. The muscular walls of the arteries expand and recoil with the beating of the heart and subsequent rise and fall of blood pressure, allowing a pulse to be felt along some arteries. The walls are composed of three layers: the tunica adventitia, or outer layer; the tunica media, or middle layer; and the tunica intima, or inner layer.
The Veins
The veins are thinner walled blood vessels that carry deoxygenated blood from the body to the heart, apart from the pulmonary vein that carries oxygenated blood from the lungs to the left atrium, as described by the Texas Heart Institute. Blood pressure in the veins is significantly lower than in the arteries. Like the arteries, the veins also have three layer walls; however, the walls contain much less muscle and elastic fiber. Veins contain valves that help to ensure that blood flows towards the heart only, and also make use of the contractions of the skeletal muscles around to help maintain blood flow.
